PROJC00189 - Laserfiche WebLink

Home Browse Search

displacement); i.e., the more fill over the pipe, the lesser is the chance of movement. This is important for a pipe under high pressure. Since water flows under atmospheric conditions in the non-pressure pipe, it will require a venting system. The two options are: stand pipes, which are normally 8 to 12 feet high With a screen at the upper end, or standard air release or air vacuum valves installed in vaults. The vented stand pipes are much less expensive; howevet, if they are used, considerable care must be used in design of the pipeline so there is assurance that the pipe section where the stand pipes are installed will not be excessively surcharged; otherwise water will flow out of the stand pipe. Intakes on Cottonwood Creek are possible with use of the non-pressure pipe; this will consist of a tee connecting the diversion pipe to the main pipe. Since there are a large number of turns and grade changes in the pipeline, it will be necessary to install a moderate number of elbows. All of these need to be protected by thruSt blocks, although the size of the thrust block will be considerably less for the non-pressure system. No in-line valves are necessary; however, one or two are suggested in case of pipe breaks. 2) Construction of F.qJll1lizing R"~rvoiT (AIL 3) This reservoir will be an off-stream reservoir and can be constructed using a cut and fill method. It should be designed so the cut balances the fill material to reduce the amount of excavation. There is a relatively flat, gently sloping site adjacent to the wye, and this is the site selected for the reservoir. The downstream embankment will be substantially higher than the upstream embankment due to the slope of the land. Observation of adjacent strealn cuts and nearby geological formations indicate that a considerable number of boulders will be encountered in the excavation. In addition, SOme ledge rock may be encountered, which will greatly increase excavation. It is assumed that the soil is relatively permeable. Therefore, an impermeable liner will be needed. It may be possible to obtain clay from nearby deposits; however, since this is not high quality clay, a thicker layer than normal may be needed (2 feet). The reservoir will be constructed as deep as possible to preserve water quality. There is less chance for algae growths with depth; however, depth will be restricted by excavation problems. V-5 I I I I I I I I I I I I I I I I I I I